A known radiation detector for two-dimensionally detecting an incident position of radiation is one having a semiconductor substrate of a first conductivity type having first and second principal faces opposed to each other and generating carriers in response to incidence of radiation, a plurality of semiconductor regions of a second conductivity type which are arranged along a position detection direction on the first principal face side of the semiconductor substrate and into which the generated carriers flow, and a plurality of semiconductor regions of the first conductivity type which are arranged along a direction perpendicular to the position detection direction on the second principal face side of the semiconductor substrate and into which the generated carriers flow (e.g., cf. Patent Literature 1).